This invention relates to a method of minimizing the size of primary silicon (Si) in Alxe2x80x94Si alloy.
Common aluminum alloys always may be classified by compositions, mechanical properties and typical applications depending upon their composing elements. Alxe2x80x94Si alloy, however, is characterized by relative high fluidity in a molten state, low contractibility and melting point, and high molding characteristics. Accordingly, recent attention has been given to Alxe2x80x94Si alloy.
According to an aluminum-silicon phase diagram, as shown in FIGURE, an Al side is an eutectic composition which consists of Si and xcex1 phase in which Si is not solidified.
Consequently, if the composition is coarse and rough, a casting material will be decreased in working ability.
In order to prevent the above disadvantage, usually phosphorus (P) has been added into molten Alxe2x80x94Si alloy so as to minimize the size of primary Si.
When phosphorus (P) is added into molten Alxe2x80x94Si alloy, Al in the molten alloy combines with P to form AlP. The formed AlP constitutes a nucleus of primary Si. It is necessary to raise the temperature of the molten alloy up to above 100xc2x0 C. from the temperature of primary crystal formation. If not so, it is difficult to form AlP.
If the temperature of molten alloy is raised excessively, a large amount of hydrogen gas is melted into the molten alloy and forms pin-holes in a casting product.
When melting aluminum alloy is poured into a metal mold at low temperature, it has the hazard of shrinkage cavities in a casting aluminum alloy.
In view of the above, a main object of the invention is to provide a method of minimizing the size of primary silicon in Alxe2x80x94Si alloy which may easily be operated and available for good casting products.
It is a further object of the invention to provide a method of minimizing the size of primary Si in Alxe2x80x94Si alloy without having shrinkage cavities in a casting product.